1.0 Field of the Disclosure
This disclosure relates generally to ammunition, and more specifically, to a reduced friction expanding bullet with improved core retention and a method of manufacturing the same.
2.0 Related Art
For a bullet to achieve optimum terminal performance, it is desirable that its jacket and core penetrate a target as a single unit and remain connected throughout the course of travel, regardless of the resistance offered by the target material.
Various attempts thus have been made over the years to form bullets wherein the bullet's jacket and core remain coupled together on impact. One of the earliest and simplest attempts utilized a knurling method which created a “cannelure” in a jacketed bullet. A cannelure typically includes a narrow, 360° circumferential depression in the shank portion of the bullet jacket. While the cannelure was originally conceived for use as a crimping feature, various manufacturers have attempted to use it as both a crimping groove and as a core retaining feature, or solely as a core retaining feature. The knurling process typically utilizes a multi-tooth knurling wheel which cuts into the jacket and forces jacket material radially inwardly, subsequently creating a shallow internal protrusion which extends a short distance into the bullet core. As a result, the jacket wall often can be weakened circumferentially in both the fore and aft areas of the cannelure. The cannelure approach thus has been found to be ineffective in keeping the core and jacket together as upon impact with a hard barrier material, the core tends to immediately extrude beyond the confines of the shallow inner protrusion, subsequently sliding out of the jacket. Depending on jacket wall thickness, core hardness, and impact energy, axial core movement can actually “iron out” the internal geometry of the cannelure as the core slides forward. In addition, when impacting windshield glass, the jacket can crack and/or be severed circumferentially along the weakened boundaries of the cannelure. Such a failure can result in jacket-core separation and a concomitant loss in bullet mass and momentum, which reduces target penetration. Even multiple cannelures have proven ineffective in retaining the core, due to the inadequate amount of square area they are collectively able to cover.
For example, U.S. Pat. No. 4,336,756 (Schreiber) describes a bullet intended for hunting. The bullet comprises a cold-worked jacket utilizing a narrow, inwardly-extending section of integral jacket material terminating in a “knife-like edge” that is formed from a thickened portion of the jacket wall and engages and holds the base of the core within the jacket after the bullet is finally formed. U.S. Pat. No. 4,856,160 (Habbe, et al.) also describes a bullet that appears to utilize a reverse taper on the rearward interior of the jacket to lock the core within the jacket.
Other attempts at retaining the core within the jacket have been used in the past. Such attempts range from providing a “partition” separating a rear core from a front core, electroplating a copper skin around the core prior to final forming the bullet, and heat-bonding (or similar heat treatment) the core to the interior of the jacket wall after the bullet is finally formed. Shortcomings of these methods can include one or more of the following: Jacket-core eccentricity resulting in less than desirable accuracy due to bullet imbalance; slower manufacturing rates; high or increased costs; and/or lower reliability.